1. Field of the Invention
The present invention relates to a throttle unit having a reduced manufacturing cost and a reduced number of man hours for assembly. Furthermore, the present invention relates to a throttle unit which is suitable for equalizing the amount of air passing through the bypass passages of the throttle valves, a bypass passage being provided for each throttle valve.
2. Description of Background Art
A throttle unit for an engine has been disclosed in Japanese Patent No. 2723990 entitled xe2x80x9cTHROTTLE BODY FOR MULTIPLE-CYLINDER COMBUSTION ENGINE.xe2x80x9d In the above document, a throttle unit is provided with a fast idling mechanism. The fast idling mechanism includes a valve for opening or closing a bypass passage for bypassing a throttle valve. The valve is provided in the bypass passage. Furthermore, when the engine is started, the valve is opened to supply air to the combustion chamber of the engine via the bypass passage to increase the number of revolution of the engine during idling to prevent the engine from unstably rotating during idling or stopping.
FIGS. 5 and 6 of the above document have been reproduced as FIGS. 7 and 8 of the present invention, respectively. In addition, for the sake of convenience, FIG. 7 of the present invention includes a portion of FIG. 4 of the above document, and FIG. 8 of the present invention includes a main portion of FIG. 6 of the above document. Furthermore, the reference numerals in FIGS. 7 and 8 of the present invention do not correspond to the reference numerals in the above document.
FIG. 7 is a first cross-sectional view of a throttle unit according to the background art which shows a state in which a throttle body 100 is provided with suction passages 101, 102, and in which the respective suction passages 101, 102 are provided with throttle valves 103, (not shown), respectively. Furthermore, the upstream side of the throttle valve 103 of one suction passage 101 is in communication with the downstream side of the throttle valve 103 of the suction passage 101 by a common bypass suction passage hole 105 and a bypass suction passage hole 106 for controlling the idling speed. The bypass suction passage hole 106 is connected to the common bypass suction passage 105. Furthermore, an idling speed control valve 107 for opening or closing the bypass suction passage hole 106 is disposed at the inlet of the bypass suction passage hole 106.
FIG. 8 is a second cross-sectional view of the throttle unit according to the background art. FIG. 8 shows a state in which a bypass suction passage hole 108 for controlling the idling speed is branched from the common bypass suction passage hole 105 (see FIG. 7) and is in communication with the downstream side of the throttle valve (not shown) of the suction passage 102. An idling speed control valve 111 for opening or closing the bypass suction passage hole 108 is disposed at the inlet of the bypass suction passage hole 108. Operating levers 112, 112 are secured to the end portions of the idling speed control valves 107, 111. Furthermore, a link shaft 113 for opening or closing the idling speed control valves 107, 111 in one operation is mounted to the operating levers 112, 112.
According to the above-mentioned technology, idling speed control valves 107, 111 are provided for each of the bypass suction passage holes 106, 108. Therefore, in addition to the idling speed control valves 107, 111, operating levers 112, 112 and parts relating to these valves are required. This increases the number of parts and therefore the number of man hours for assembly and the manufacturing costs of the throttle unit are increased.
Furthermore, since the plurality of idling speed control valves 107, 111 are opened or closed by one link shaft 113 via the operating levers 112, 112, depending on the variation in the size of the idling speed control valves 107, 111, the operating levers 112, and the link shaft 113, there is the possibility that a difference in the opening of the idling speed control valves 107, 111 may be produced to make the amount of air passing through the respective bypass suction passage holes 106 different from the amount of air passing through the respective bypass suction passage holes 108. Accordingly, the number of revolution of the engine during idling may become unstable.
For the above reason, the object of the present invention is to reduce the manufacturing costs and the number of man hours for assembly of the throttle unit of an engine and to equalize the amount of air passing through the bypass passages for each of the throttle valves.
In order to accomplish the object described above, according to a first aspect of the present invention, in a throttle unit of an engine including suction passages from an air cleaner to the respective combustion chambers of a multiple-cylinder engine, throttle valves disposed in the respective suction passages, and bypass passages bypassing the throttle valves, the bypass passage includes an inlet of the bypass passage communicating with the upstream side of the throttle valve of the suction passage, one valve body receiving chamber coaxial with the inlet of the bypass passage, a plurality of upstream side branch passages extending from the valve body receiving chamber, downstream side branch passages extending from the end portions of the upstream side branch passages and communicating with the downstream sides of the throttle valve of the suction passage, one valve body which is movably received in the valve body receiving chamber and is moved in the valve body receiving chamber in the direction away from the inlet of the bypass passage to open the plurality of upstream side branch passages at the same opening when opening the bypass passage.
In the throttle unit according to the background art, a bypass passage for bypassing a throttle valve is disposed in each suction passage sending air into the combustion chamber of each cylinder and a valve for opening or closing the bypass passage is disposed at each bypass passage and a link mechanism is disposed at each valve to activate the valve. For this reason, in the throttle unit according to the background art, the number of parts increases and the manufacturing cost and the number of man hours for assembly of the throttle unit increase. However, according to the-present invention, a mechanism for activating the bypass valve can be simplified by reducing the number of the bypass valves of the multiple-cylinder engine to one. This can reduce the manufacturing costs and the number of man hours required for assembly of the throttle unit.
Furthermore, during the control of the opening or closing of the bypass passage by one valve body in the throttle unit according to the background art, suction air tends to be sucked into one cylinder from the other cylinder by a difference in negative pressure between the respective cylinders. However, by controlling the opening of each of the plurality of upstream side branch passages to be at the same opening, it is possible to make the total sum of the opening areas of the upstream side branch passages smaller than the passage area of the inlet side of the bypass passage at a time when the number of revolutions of the engine is not more than 2000 rpm and tends to vary widely.
Accordingly, it is possible to prevent the suction air from being sucked into one cylinder from the other cylinder and therefore prevent a variation in the number of revolutions of the engine. Therefore, it is possible to control the number of revolutions of the engine during idling with a high accuracy.
According to a second aspect of the present invention, the plurality of upstream side branch passages are formed on a line crossing at right angles and passing through the valve body receiving chamber.
The plurality of upstream side branch passages can be easily formed in one machining step to reduce the time and cost of machining.
According to a third aspect of the present invention, the valve body receiving chamber has a diameter larger than the inlet of the bypass passage. Furthermore, the valve body is butted against a step-wise portion between the valve body receiving chamber and the inlet of the bypass passage to completely close the bypass passage.
The above-mentioned construction according to the third aspect of the present invention can minimize the amount of air leakage when all of the bypass passages are closed and can more correctly conduct suction control except when the engine is being started.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.